Homocysteine (Hcy) is a sulfur-containing amino acid with its only source in the human body being methionine. Three B complex vitamins (B 6 , folate or B 9 , and B 12 ) participate in the metabolism of Hcy. Deficiency of these vitamins and the enzymes involved in its metabolism leads to elevated plasma Hcy levels (normal 5 - 15 μmol/l). Hyperhomocysteinemia (HHcy) is associated with several disorders. Hcy levels above 50 μmol/l is thought to be a risk factor for recurrent heart attacks and a value between 150 and 200 μmol/l may cause ischemic stroke. Levels above 300 μmol/l may induce mental deficiency. Several factors contributing to HHcy have been identified. These include lifestyle factors (smoking, alcoholism), drugs (phenytoin, valproate) and genetic causes (cystathionine β synthase deficiency). The various manifestations of HHcy are explained on the basis of oxidative damage and protein homocysteinylation, which cause damage to most tissues/organs leading to health complications and occurrence of various diseases. HHcy may affect major systems in the body like cardiovascular (coronary artery disease, myocardial infarction), central nervous (cerebrovascular accident, Alzheimer's, dementia) skeletal (increased risk of fractures), renal (low GFR), reproductive (risk of infertility), besides increasing the risk of hypothyroidism and cancer. The measures to prevent HHcy include consumption of nutritious foods, lifestyle changes (avoidance of smoking and alcohol) and supplementation of diet with vitamins - B 6 , folate or B 9 , and B 12 .